Hooman Tafreshi

This proposal combines the capabilities of the academic partner (NCSU) with those of the business partner (O&M Halyard) to develop ultra-low-pressure-drop media for PPE. NCSU Role: Explore the use of high-density dies with smaller capillaries (the state of the art is 35 to 45 holes per inch with 300 µm capillaries). NCSU will explore dies with 60 holes per inch (having 300 and 250 µm capillaries) and dies with 75 holes per inch (having 180 µm capillaries). NCSU will also explore using dies with 6 inch segments having different hole diameters (e.g., 250, 200, 175, 150, 150, 175, 200, and 250 µm) but a constant hole density as well as 6 inch segments having different hole densities but a fixed hole diameter. Such novel die designs can potentially lead to creation of nonwovens with multimodal fiber diameter distributions (known to help lower the pressure drop). O&M Halyard Role: O&M Halyard will conduct trials to evaluate hydro-charging of the MB filter media on the pilot line at Reifenhauser. In this case, the MB nonwovens containing the additives based on developed chemistry will be made and hydro-charged in-line and then compared to the MB nonwovens made off-line by NCSU and hydro-charged at Reifenhauser or on the hydro-charging equipment that will be built by NCSU. All hydro-charged MBs will be compared to their corona-charged counterparts for their filtration efficiency. Process parameters will be varied to achieve different nonwoven structures at different basis weights of 15, 20, 30 g/m2, mean fiber size of 1, 2, 4 and 6 µm, and low, medium, and high nonwoven loft (density) to study the impact on filtration performance and pressure drop (per N95 product constructions). In addition, O&M Halyard will evaluate different MB die tips separately (45 and 75 holes per inch tip density) and in-line (40 and 60 holes per inch tip density) available on the Reifenhauser pilot line to study the impact of MB die tip density on the filter properties, and also in combination with the hydro-charging. This study would supplement the work of NCSU on their high-density MB die tips. O&M Halyard and NCSU will also carry out filter-aging studies for the charged media to determine the long-term pros and cons of hydro- and corona-charging processes.

We need a new paradigm for manufacturing bio-based MB and SB structures used in PPE and must be able to increase capacity without the need for new facilities. Our vision is to create a new platform made from a biopolymer such as Polylactic Acid (PLA) and polyhydroxyalkanoate (PHA). PLA is a renewable polymer and is produced in the US (now also in Europe and Asia) in large quantities. The PLA is used in many products but not in nonwovens. However, it provides a significant opportunity in terms of environmental sustainability as well as increasing the capacity. The goal is to deliver a SMS structure made from PLA/PHA/PBS or their blends that can be used in both gowns and facemasks. This new platform can be transferred to existing production lines and can more than double the capacity of available materials for PPE while offering environmental sustainability.

This proposal combines the modeling expertise of the academic partner (NCSU) with the manufacturing and testing capabilities of the business partner (KCC) to develop ultra-low-pressure-drop aerosol filters for PPE and HVAC systems. NCSU will be responsible to design optimization of the filter microstructure and charge density (using in-house computer codes and artificial intelligence tools). KCC will be responsible for conducting trials for manufacturing the media, charging the media, and testing them as PPE and HVAC filters.

Our goal is to understand how thermally unstable particles, like metal organic frameworks (MOFs), can thermally be bonded to spun fiber streams via a coforming process. We seek to take advantage of the tackiness of polymer melt post extrusion and the ability of electrostatically charged polymer to attract particulate matter. With this, we hope to incorporate thermally sensitive and high value targets to fibers to increase functionality and value.

With the industry becoming increasingly more computational, developing tools for virtual material design is now becoming a necessity. In this context, we propose to develop a computational tool to simulate the 3-D microstructure of a nonwoven fabric during compression–recovery cycles. This is significant as nonwovens’ compression–recovery behavior can affect their performance in a variety of applications where the material is subject to normal/shear loads. We propose to develop a new modeling approach in which the fibers are treated as arrays of beads connected to one another with springs and dampers, referred to here as the mass-spring-damper (MSD) model. This approach allows us to simulate how a mechanical load propagates inside a nonwoven structure. The simulations will be conducted through accurate modeling of force transfer (normal and tangential stresses) between the fibers at the fiber–fiber contact points. The fibers will be allowed to bend (e.g., at fiber–fiber crossovers) according to their physical properties (e.g., bending rigidity) and according to the local stress values in the structure.

This proposal is prepared to improve our understanding of how electrically charged nonwovens remove dust particles from a surface (as in electrically charged dry wipes), or from air (as in electrostatically charged aerosol filters). Interestingly, the underlying physics of removing a particle from air using a charged filter (e.g., the popular N95 masks) is not very different from that of removing a particle from a surface using an electrically charged dry wipe. Regardless, quantifying the attraction/repulsion forces between a charged nonwoven and a particle has remained an unsolved challenge. This knowledge gap has prevented manufacturing of such products through engineering design, leaving laborious trial-and-error as the only viable option.

Droplet filtration using coalescing filters, fluid absorption in diapers, fluid release from wet wipes, fluid penetration in barrier fabrics or fibrous membranes are a few examples of industrial applications where quantifying the rate of fluid transport in a partially-saturated nonwoven is crucial for product development/optimization. This proposal presents a new experimental approach for studying fluid transport in nonwovens. While the proposal is developed primarily for coalescing filters, the outcomes of this study can directly be applied to other applications (diapers, wet wipes, membranes…). Filters that remove droplets from a flow (a gas or a liquid flow) are referred to as coalescence filters. Such filters are used, for instance, in filtering oil droplets from fume gases or in removing dispersed water droplets from diesel/oils, among other applications (e.g., food, pharmaceutical…). Coalescence filters collect such dispersed droplets and allow them to coalesce with one another. Once the droplets are large enough, they will drain from the filter under the influence of gravity. At their steady operation, coalescence filters are partially-saturated (partially-wetted) with the droplets they collect. The biggest challenge in designing a nonwoven media for coalescence filtration (or for diapers or wipes) is predicting its transient or steady-state saturation during the operation. Knowing the wetting saturation of a filter, it will be relatively easy to predict its collection efficiency. In this project, we will use a centrifugal force to drive the droplets through the filtration media. This is different from the traditional coalescence filtration experiments where a gas has been used as the driving force. We hypothesize that with a centrifugal force, one can better isolate the role of nonwovens’ microstructure in promoting/preventing fluid transport. This new approach allows us to develop universal relationships for the wetting saturation of a nonwoven in terms of its microstructural properties, something that cannot be achieved following the traditional testing method.

The COVID-19 pandemic has highlighted a lack of protective equipment not only in high-risk hospital settings, but also in non-hospital settings which require close contact with patients such as ophthalmology, optometry, dentistry, and others. The protection factor of N95 masks and plastic face shields are not sufficient in these settings, and a more protective device is required. The goal of this project is to develop a breathable film or fabric that can serve as a platform technology for multiple form factors, such as powered air purifying respirators. This project will focus on improving the protective factor of such devices while keeping costs low enough to support wide deployment in the fields mentioned above. Usability, performance, and cost will be primary factors governing design and manufacturing decisions.

Natick is interested in facemasks for warfighters that have a good fit, are easy to breathe through during normal level of physical activity, are easy to manufacture and can potentially be laundered and reused. Most current technologies use an electrostatically charged meltblown fabric. These are made from polypropylene and are rather fragile and cannot be reused, laundered, die cut or handled alone during manufacturing. Keeping all of these criteria in mind, NWI proposes developing two options, 1) a disposable simple spunbond single or double-layer spunbond facemask and 2) a reusable shell with a spunbond filter insert